Solvent extraction of coal

ABSTRACT

COAL IS CONVERTED TO LIQUID PRODUCTS UTILIZING A TWOSTAGE SOLVENT EXTRACTION PROCESS WHEREIN THE LIQUID COAL PRODUCTS ARE SEPARATGED FROM UNREACTED COAL AND ASH WITHOUT REQUIRING FILTRATION. THE COAL IS FIRST CONTACTED WITH CONVENTIONAL COAL SOLVENTS, SUCH AS TETRAHYDRONAPHTHALENE UNDER HYDROGEN PRESSURE; THE SOLVENT IS REMOVED VIA FRACTIONATION; AND HYDROGEN-RICH COAL COMPONENTS PRODUCED ARE RECOVERED FREE OF PARTICULATE MATTER BY SOLVENT EXTRACTION WITH A LIGHT AROMATIC OR KETONE SOLVENT.

Aug. 10, 1971 W. K. T. GLEIM ETAL soLvENT EXTRACTION 0F com.

Filed' Aug. 18, 1969 /N V EN T O R5* W//Ham K. T Gle/'m f Ric/70rd S. Gorey Frederick J. R/'ed/ George R. Sun age/ O? #Mwgs' life/bf @l ufff/UK A T T O /V E YS United States Patent O 3,598,718 SOLVENT EXTRACTION OF COAL William K. T. Gleim, Island Lake, Richard S. Corey, Rolling Meadows, Frederick J. Riedl, Arlington Heights, and George R. Sunagel, Mount Prospect, Ill., assignors to Universal Oil Products Company, Des Plaines, Ill. Continuation-impart of application Ser. No. 739,838, June 25, 1968. This application Aug. 18, 1969, Ser. No. 850,987

Int. Cl. ClOg 1/00 U.S. Cl. 208-8 14 Claims ABSTRACT OF THE DISCLOSURE Coal is converted to liquid products utilizing a twostage solvent extraction process wherein the liquid coal products are separated from unreacted coal and ash without requiring filtration. The coal is first contacted with conventional coal solvents, such as tetrahydronaphthalene under hydrogen pressure; the solvent is removed via fractionation; and hydrogen-rich coal components produced are recovered free of particulate matter by solvent extraction with a light aromatic or ketone solvent.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application Ser. No. 739,838 filed June 25, 1968.

BACKGROUNDv OF INVENTION This invention relates to a process for converting coal to liquid products. In particular, this invention relates to a process for converting coal to liquid products using a dual, selective solvent system wherein unconverted coal and ash are readily separated from val-uable coal products without utilizing filtration techniques.

Coal represents a valuable source of energy to the world, particularly since it appears that known coal and lignite deposits are an order of magnitude greater than known petroleum reserves. As these petroleum reserves are depleted andthe need for liquid hydrocarbon increases, it becomes imperative that methods for converting coal to liquid products be developed.

Several methods capable of converting coal to more valuable liquid products are known to the art. One of these methods employs gasification techniques such as destructive distillation to effect the conversion of the coal. Another, more recently developed method, involves high pressure hydrogenation techniques. Still another re cently developed technique involves solvent extractionA under H2 pressure, a technique related to the process of the present invention.

ln the prior art solvent extraction processes, crushed, rather finely divided particulate coal is contacted with a selective solvent system which serves, at least in part, as a hydrogen donor as well as a solvent for the conversion of the hydrogen-deficient coal to liquid prod-ucts. Following this extraction step, the prior art filters out the undissolved, solid particulate matter, recovering therefrom a solid free liquid coal extract-solvent mixture. The liquid coal extract is then recovered, typically by fractionation and is further processed by conventional hydrocarbon processing techniques such as coking, cracking, hydrogena4 tion, etc., to convert the liquid coal extract into more valuable and useful products.

One of the main difficulties encountered in the prior art solvent extraction processes is in separating the liquid coal extract from the undissolved coal, ash and other solid, inorganic, particulate matter. Under the conditions utilized in the extraction step, the solid coal dispersed in the Patented Aug. 10, 1971 liquid phase is in a very fine physical state which, because of the tine particle size of the coal and the physical prop erties of the solvent-liquid coal extract, renders physical separation difficult. The extremely fine solid particles are not readily removed by settling or centrifuging techniques and as a result cause problems in further processing, particularly those processing steps employing fixed-bed catalytic reactors. These fine particles are, however, capable of removal by filtration techniques such as those utilizing pre-coated filters at both ambient temperatures and pressures as well as at higher temperatures and pressures. These techniques, however, are not completely satisfactory in a practical, economical sense since the paper, fabric, or cake used for the filtration is readily obstructed, thus requiring continuous replacement.

Another problem confronting the prior art is the nonselectivity associated with the solvent extraction since the solvents typically utilized accomplish essentially total solution of the coal without regard to selectivity for the higher value, higher hydrogen content components or the lower value, lower hydrogen content components. In essence, the solvents typically utilized indiscriminately produce a coal extract containing both high hydrogen content and low hydrogen content components.

SUMMARY OF lTHE INVENTION Accordingly, it is an object of this invention to produce an ef'lcient method for converting coal to valuable liquid products via a solvent extraction technique. It is a particular object of this invention to provide a solvent .extraction process wherein undissolved coal, ash, and inorganic materials present at the termination of the extraction reaction in intimate admixture with the liquid coal products and solvent are readly removed from these liquid coal products. It is a further object of this invention to provide a solvent extraction process wherein the higher value, high hydrogen content components present in the liquid coal extract are readily recoverable from the lower value, low hydrogen content components.

It has now been discovered that the higher value, high hydrogen content liquid coal components present in admixture with undissolved coal particles, ash, etc., at the completion of a conventional solvent extraction process utilizing conventional solvents such as Tetralin (Dupont trademark for tetrahydronaphthalene) are readily separable from the lower value, low hydrogen content components of the liquid coal extract. This dual separation is accomplished by removing at least a portion and preferably the entire solvent from the liquid coal extract by conventional means, such as distillation, and treating the resultant residue with a selective light monocyclic aromatic, a cyclohexane, or ketone solvent. This selective solvent selectively removes the high hydrogen content components from both the low hydrogen content components and the undissolved coal, ash, and solid inorganic materials rendering a solid free, high hydrogen content liquid phase.

In an embodiment, this invention thus relates to a process for the conversion of solid, ash-containing coal particles into liquid products which comprises the steps of: (a) contacting said coal with a rst solvent in a first contacting zone under hydrogen pressure and extraction conditions to produce an efliuent containing a liquid coal extract comprised of hydrogen-rich components and hydrogen-lean components in admixture with said solvent and unconverted coal and ash particles; (b) separating from said eluent at least a portion'of said rst solvent to produce a stream of coal extract in admixture with at least a portion of said unconverted coal and ash particles; (c) contacting said stream with a second solvent selective for said hydrogen-rich coal extract components in a second contacting zone at extraction conditions to.

produce a second zone eluent containing a hydrogenrich liquid phase and a lhydrogen-lean liquid phase; and, (d) separating from said second zone eluent a hydrogenrich liquid phase and a hydrogen-lean liquid phase, said second zone hydrogen-rich liquid phase being essentially free of unconverted coal and ash particles.

In a further embodiment this invention relates to a process for the conversion of ash-containing solid coal into liquid products which comprises the steps of: (a) admixing coarse size coal with a iirst solvent capable of converting coal to liquid products thereby providing a solvent-coarse coal mixture; (b) passing said mixture to a. pulverization zone maintained at pulverization conditions including a temperature of about C. to about 200 C., a pressure of about atmospheric to about i000 atmospheres, a solvent to coal weight ratio of about 0.2

to about 10.0, said pulverization conditions suiiicient to produce a pulverized coal-solvent product wherein at least a portion of said coarse coal is reduced to about at least a minus 8 Tyler standard screen size; (c) passing at least a portion of said coal-solvent product to a coal conversion zone maintained at coal conversion conditions and under hydrogen pressure so as to produce `a liquid coal extract product containing unconverted coal, ash,

and solvent wherein an excess of 50 weight percent of the MAF coal is converted to hydrogen-rich components and hydrogen-lean components; (d) separating from said product at least a portion of said irst solvent to produce a stream of coal extract in admixture with at least a portion of said unconverted coal and ash; (e) contacting said stream'with a second solvent selective for said hydrogen-rich liquid coal components in an extraction zone to produce an extraction zone eflluent containing a hydro- Vgen-rich liquid phase and a hydrogen-lean liquid phase; and, (f) separating from said extraction zone eflluent a hydrogen-rich liquid phase and a hydrogen-lean liquid phase, said hydrogen-rich liquid phase being essentially free of unconverted coal particles and ash.

In further more limited embodiments, the foregoing rst solvent is a polycyclic aromatic including aromatic, naphthenic hydrocarbons such as Tetralin and the second solvent is either a monocyclic aromatic such as ben.- zene, a naphthene such as cyclohexane, or a ketone. Further limited embodiments and processing conditions will be found in the following more detailed description of the invention.

Thus, the process of this invention utilizes a novel, two-stage solvent extraction technique wherein particulate coal is rst contacted with a lirst solvent to produce a liquid coal extract-solvent-undissolved coal mixture. From this mixture, the solvent is removed and the resultant mixture contacted with a second solvent to produce a lhydrogen-rich, solids-freephase readily separable from a hydrogen-deficient, solids phase.

DESCRIPTION OF PREFERRED EMBODIMENTS The coal preferably utilized in the process of the present invention is bituminous coal such as Pittsburgh seam coal. More preferably, this bituminous coal has a high Ivolatile content, typically having a volatile content greater than about by weight of the moisture and ash-free (MAF) coal.

Preferred solvents for use in the first stage extraction step of the process of the present invention are those which are of the hydrogen donor type and which are at least partially hydrogenated such as the naphthenic-aromatic hydrocarbons. Preferably, the rst stage solvent is one which is in the liquid phase at the recommended temperature and pressures utilized in the extraction and/ orV pulverization step of this process. Typically, those solvents are employed in mixtures of hydrocarbons and are derived, at; least in part, from the intermediate or final products obtained from subsequent processing following the practice of this invention.

Typically, these first stage solvent hydrocarbons or mixtures of hydrocarbons boil between about 200 C. and about 425 C. Examples of such preferred naphthenicaromatic rst stage solvents are the dior tetra-, hydro derivatives of anthracene and phenanthrene. Also preferred are the aromatic hydro derivatives of naphthalene such as tetrahydronaphthalene (Tetralin). As used herein, naphthenic-aromatic solvents refer to polycyclic compounds wherein at least one of the rings is aromatic and at least one of the rings is not aromatic.

Also applicable within the process of this invention are the completely aromatic polycyclic aromatic compounds such as biphenyl, the methylnaphthalenes, the dimethylnaphthalenes, mixtures of phenanthrene and anthracene, etc., as well as their alkyl derivatives. Other types of solvents which may be utilized as rst stage solvents include phenolic compounds such as phenols, cresols, and xylenols, particularly when utilized in admixture with any of the foregoing solvents. In general, the partially hydrogenated aromatic compounds are preferred over the cornpletely aromatic polycyclic hydrocarbons. In any event, the solvent suitable for use in the rst stage extraction zone must be a solvent having the ability to depolymerize the pulverized coal during this extraction step.

A particularly preferred embodiment of the process of the present invention includes the use of a selective solvent of the type hereinbefore described for use in the rst stage extraction zone during the pulverization step whereby relatively coarse size coal is reduced to granular coal of optimum size for the extraction step. This preferred embodiment is predicated on the theory that having the presence of a hydrogen-rich solvent during the pulverization step of the coal results in a substantial increase in the efficiency of the operation and in many cases results in a decreased use of the rst stage solvent for `obtaining the same quality and quantity of liquid-coal extract.

The benefit gained from having the solvent present during the pulverization step appears to be the result of an extremely reactive shear point during the crushing and grinding of the coal. In other Words, the shear site is extremely reactive and hydrogen can be transferred to the coal at that site more easily when the solvent is present than when the coal is pulverized in the absence of the solvent. In addition, the small particles of coal thus sheared away from a large lump are not only exposed to a highly reactive shear site, but also immediately expose a relatively large surface area to the solvent, enabling the small particles of coal to be almost immediately exposed to the solvent and wetted thereby facilitating the penetration of the solvent into the coal particle.

Apparatus for use in pulverizing lump or coarse size coal as practiced in the process of the present invention may be of any type known to those skilled in the art. Conventional ball mills or rod mills may be used with satisfactory results. Preferably, the apparatus must be able to pulverize lump or coarsecoal in the presence of significant quantities of liquid solvent without diculty. Those skilled in the art are familiar with the kind of apparatus required for processing wet solids and the ciushing and grinding thereof so that no detailed discussion of these apparatus need be presented herein. The prime requirement for crushing and grinding of the lump coal is that the coarse coal, usually -have an average particle diameter in excess of 0.08 inch Vand typically about 0.25 to 2.0 inch, must be processed and reduced in size to an average particle diameter equivalent to at least a -14 Tyler Screen Size. As used herein, the terms Tyler screen refers in all instances to the commercial Tyler standard screens. The correlation between Tyler screen size and particle size can be found in most standard reference books such as Perrys Chemical Engineers Handbook, fourth edition, pages 2l-5l.

The conditions utilized during the pulverization step may be varied widely in practicing this present invention according to the desire of those skilled in the art. The temperature may be varied over a relatively broad range, from essentially ambient temperature to a relatively high processing temperature. It is distinctly preferred, however, for the practice of this invention that the temperature of the coal and solvent be maintained at a temperature such as from about C. to about 200 C. The pressure, in a similar manner, may be varied over an extremely wide range of from atmospheric pressure to about 1,000 p.s.i.g. with a preferred pressure being about 100 p.s.i.g. This pressure is preferably maintained by the utilization of a hydrogen-containing gas. In any event, it is preferred that the pressure be of such degree to maintain the solevnt in the liquid phase during the pulverization and extraction steps.

The operation of the pulverization equipment is preferably performed in a manner such that the oversized material; that is, that material greater in size than about a -8 to -10 Tyler screen size, be separated and returned to the pulverization apparatus for further reduction in particle size. The utilization of such a closed circuit technique is well known to those skilled in the art and is preferred for the practice of this invention to insure a most optimum and complete utilization of the solid coal. Unless otherwise stated, a closed circuit recycle operation of the pulverization equipment Will be deemed inherent in the practice of the process of the present invention. Itis to be noted that this separation is readily accomplished without difliculty since only the coarse, larger size coal particles are removed and recycled. The ner particulate coal is not to be removed since it is to be subjected to further extraction. This coarse size removal can be readily accomplished by gravity type separations including hydroclones, centrifuges, etc.

The amount of solvent to be utilized in the rst stage extraction zone utilized in the present process and which includes the pulverization zone when a solvent is utilized therein as well as the digestion zone generally will range from about 0.2 to pounds of solvent per pound of coal. Satisfactory results are obtained in utilizing approximately a 1:11 to 3:1 solvent to coal ratio on a weight basis. In the practice of the preferred embodiment of this invention, conditions utilized during the pulverization step should be chosen so that the coarse coal is reduced in size to at least a -8 Tyler screen size.

The extraction of coal by means of solvent extraction is basically a partial conversion of the coal as well as an extraction since not only is the coal reacted with the hydrogen, which is preferably transferred from the solvent,

but there is also a solution phenomena which actually diso solves the coal which has accepted the hydrogen from the solvent phase. Therefore., as used herein, the terms liquidcoal extracts, extracted coal fraction, extracted coal, or other words of similar import, are intended to include the liquid product which is obtained from the various steps utilized in the practice of the process of the present invention and, generally, will be described on the basis of being solvent-free, even though a portion of the inal liquid-coal extract following the second extraction step comprises hydrocarbons suitable for use as the selective solvent in the iirst extraction zone. Preferably, the practice of the present invention in both the extraction zones is performed under conditions which increase the kinetics of the solvation reaction while maintaining the components therein in primarily the liquid phase, although in some cases it may be desirable to practice the rst step of the extraction operation in the presence of a vaporized solvent using a gaseous extraction technique.

As stated, the iirst extraction zone includes pulverization of the large coal to smaller particulate coal in either the presence or absence of solvent as well as a digestion zone wherein the coal is either initially contacted with solvent if none were present during the pulverization step or, more preferably, where the etlluent from the pulverization step where solvent was utilized is allowed to fully extract the coal to form a liquid-coal extract. The operating conditions for the digestion zone include a temperature from about 300 C. to about 500 C., a hydrogen pressure from about atmosphere to 10,000 p.s.i.g., a solvent to coal weight ratio from about 0.2 to about l0, and a residence time from about 30 seconds to 5 hours, so correlated as to dissolve in excess of 50% by weight of the MAF coal and to convert this coal to liquid products.

It is to be noted the temperature and/ or pressure utilized during the digestion step may be the same, higher, lower, or any different configuration desired by those skilled in the art over those conditions maintained in the pulverization zone. It is preferred in the practice of the process of the present invention to maintain the temperature in the digestion zone at substantially higher levels than those temperatures and pressures utilized in the pulverization zone.

Since the purpose of the digestion zone, including the process of the preferred embodiment wherein a iirst solvent is utilized in the pulverization and digestion zones, is to substantially complete the conversion of solid coal into a liquid-coal extract, it is desirable to add to this digestion zone additional solvent, a hydrogen-containing gas, and/or a hydrogenation catalyst to the digestion zone. If such a catalyst is required or desired, it may be of a conventional hydrogenation type and may be used either homogeneously or heterogeneously. Thus, this catalyst may be introduced into the pulverization zone and/ or digestion zone in admixture with the liquid first selective solvent or with the solid particulate coal. Those skilled in the art having a `knowledge of the characteristics of the coal, solvent utilized, and property desired for the final coal product can determine from the teachings presented herein the desirability to use any or all of these enumerated features in the pulverization and/or digestion zones.

Examples of conventional hydrogenation catalysts which may be used in the rst extraction zone include cobalt-molybdate and nickel-molybdate, nickel-tungstate, and any other hydrogenation catalyst capable of operation in the presence of sulfur-containing coal charge stocks. These catalysts are applicable to the solvent-coal system environment maintained in the rst extraction zone, including a slurry catalyst system and a homogeneous catalyst system. The hydrogenation in the digestion zone generally accomplishes the transfer of hydrogen directly to the coal molecules, the transfer of hydrogen to hydrogen donor molecules to coal molecules, and any combination of the foregoing. In any event, the resultant digestion zone eiiiuent has at least a portion of the first solvent removed therefrom and the resulting liquid-coal, undissolved coal, ash, catalyst (if present), etc., mixture is contacted in a second extraction zone with the following described second selective solvent. It is to be noted that it is within the scope of the process of the present invention to remove a portion of the foregoing solid particles from the digestion zone eiuent, particularly the coarser, denser particles readily removable by conventional solid-liquid separation means, preferaby hydroclones, centrifuges, etc. In any event, it is not necessary to remove all the particles including the finer ones since they will be ultimately removed from the liquid product via the hereindescribed second extraction zone, thus avoiding the cumbersome filtration steps heretofore utilized by the art to effect removal of fine particulate matter.

Suitable preferred solvents for use in the second stage extraction zone belong to the broad class of compounds known as ketones, and, in addition, the monocyclic aromatic hydrocarbons and their naphthenic derivatives. Examples of ketones which may be used satisfactorily in the second stage extraction zone include acetone, methylethylketone, methylbutylketone, methylisobutylketone, dibutylketone, etc. Other suitable solvents, as staged for use in the second stage extraction zone include the monocyclic aromatic hydrocarbons such as benzene, toluene, xylenes, etc., and the corresponding cyclohexanes. It is to be noted by those skilled in the art that these classes of secondary extraction solvents have no substantial effect on the conversion of the solid coal to a liquid coal extract. Therefore, it is a requirement of the present invention that the first stage extraction zone utilize those solvents which are applicable to the conversion of solid coal particles to the liquid form and that the second stage extraction zone solvents be limited to those solvents which serve to separate the hydrogen-rich components from the hydrogen-lean components and undissolved coal, etc., contained in the liquid-coal extract produced in the rst extraction zone. In other words, it has been found that the ketones, monocyclic aromatics, cyclohexanes, and alkylcyclohexanes are selective for the hydrogen-rich cornponents to the substantial rejection of the hydrogen-lean components and undissolved coal and ash. The exact choice of selective solvent depends on the extraction conditions desired in the second extraction zone. For practical purposes, the temperature selected for the second extraction zone should be at least 30 C. below the critical temperature of the second stage extratcion zone solvent in order to maintain the components, with the proper pressure, in primarily the liquid phase. In general, the temperatures utilized for the second stage extraction zone should not exceed 300 C.

The operating conditions to be utilized in the second stage extraction zone utilizing the ketone, monocyclic aromatic or cyclohexane solvent include a temperature from about 50 C. to about 300 C., and more preferably from about 50 to about 150 C., a H2 pressure from about 100 p.s.i.g. to about 1000 p.s.i.g., and more preferably from about 350 p.s.i.g. to about 700 p.s.i.g., a solvent to feed ratio from about 0.5 to about by weight, a liquid hourly space velocity from about 0.5 to about 5, and in the presence of a hydrogen-containing gas in an amount from about 500 standard cubic feet to about 5000 standard cubic feet per barrel of liquid feed present in the second extraction zone. These conditions are su'icient to substantially separate, on a selective basis, the hydrogen-rich components from the hydrogen-lean component contained in the liquid feed passed to the second extraction zone from the first extraction zone.

The liquid-coal extract obtained from the first extraction zone will contain compounds of widely varying physical characteristics since the first extraction step is relatively non-selective. However, the liquid coal extract may be characterized as being composed of basically two liquid fractions, namely a hydrogen-rich fraction and a hydrogen-lean fraction. As used herein, the term hydrogen-lean component or Words of similar import are intended to include those components which are basically insoluble in benzene or cyclohexane. These hydrogenlean components typically have an average molecular weight of about 1000 to 5000 and contain about 3% to about 5% by weight hydrogen. On'the other hand, as used herein, the term hydrogen-rich components or other words of similar import are intended to include those components which are basically soluble in benzene or cyclohexane. These hydrogen-rich components typically have a molecular weight of less than 1500 and more typically from about 300 to 1000 and have a hydrogen content on a weight basis in excess of 5% and typically have a hydrogen content from about 6% to 9% by weight. The above characteristics of the two major fractions contained in the liquid extracted coal are, of course, influenced to some extent by the solvent extraction conditions utilized in the f tirst stage extraction zone including the depth of extraction employed in this rst step. It is to be recognized that the hydrogen-lean components characteristic of the liquid-coal extract will only be influenced slightly by the extraction conditions but will be considerably influenced by the type of coal utilized as a feed to the process of the present invention.

In any event, after the liquid-coal, extract-solid coal mixture is contacted with the foregoing second selective solvent, a two-phase liquid system results. An upper phase containing the hydrogen-rich liquid coal components (typically 6ft-901% of the liquid coal formed) and essentially free of undissolved coal, ash, etc., (i.e., less than 0.5 wt. percent solids) is separated from a lower phase containing the hydrogen-lean, liquid-coal components in admixture with any undissolved coal, ash, etc. This hydrogen-lean, solid coal slurry is removed from the second extraction zone for use as fuel or for the conversion thereof to relatively pure hydrogen by the use of the watergas reaction. The thus produced hydrogen may then be utilized within the process of the present invention as hereinbefore described. The rich solvent from the second extraction zone comprising either the ketone, cyclohexane, or monocyclic aromatic hydrocarbon having dissolved therein the hydrogen-rich components is further processed by means well known to those skilled in the art such as fractionation, hydrogenation, hydrocracking, etc., in order to separate and convert the liquid-coal extract into more valuable products such as relatively light hydrocarbons, relatively heavy hydrocarbons, chemicals, fuels, etc., the utility of which are well known to those skilled in the art. As previously mentioned, a portion of these separated products from the liquid-coal extract may be satisfactorily utilized as at least a portion of the first selective solvent utilized in the first extraction zone.

In summary, therefore, the process of the present invention thus entails reducing coal to a line, particulate size either in the presence or absence of a rst solvent, converting the majority of said particulate coal in presence of a first solvent to a liquid-coal product of hydrogen-rich and hydrogen-lean components in admixture with undissolved coal and rst solvent, and treating said mixture after removal of at least a portion of the first solvent with a second solvent to produce a hydrogen-rich, undissolved, coal-free phase for further processing.

This process may be more fully understood with reference to the appended schematic apparatus and ow diagram illustrating the practice and details of the preferred embodiments of the process of the present invention.

BRIEF DESCRIPTION OF THE DRAWING Referring to the appended drawing, coarse coal having an average particle diameter generally in excess of 0.08 inch and usually less than 2.5 inches is introduced into the process via line 1. A suitable selective rst solvent with an enriched hydrogen content, such as Tetralin, is introduced via line 2 and admixed with the fresh feed coarse coal entering from line 1. Over-sized solid material resulting from incomplete size reduction in the hereinafter described pulverization zone is recycled to the pulverization zone via line 3 and admixed with fresh coal and solvent. This entire admixture of coarse coal and rst selective solvent is passed via line 4 into mill 5 which may be of the conventional ball mill type adapted for use in the presence of a liquid according to means well known to those skilled in the art.

Suitable pulverization conditions such as a temperature of about C., a pressure of about 70 p.s.i.g., and a solvent to coal weight ratio of about 2.0 are maintained in mill 5 such that the coarse coal is reeduced to an average particle diameter between about 0.08 and about 0.04 inch.

The effluent from mill 5 containing Tetralin and undissolved coal of proper small particle size and undissolved, oversized coal is passed via line 6 into first separator 7 which may be of the hydroclone type. Conditions are maintained in separator 7 whereby the oversized coal particles, preferably, in admixture with at least a portion of the liquid material, are removed via line 3 and returned to mill 5 as previously discussed.

The lirst selective solvent, Tetralin, plus line, undissolved pulverized coal is removed from rst separator 7 via line 8 and is admixed with a hydrogen-containing gas entering from line 10, and the total mixture is passed via line 8 into digestion zone 11 which may be a jacketed, stirred type vessel. Added Tetralin solvent, if any, may be introduced into the system via line 9 in an amount suicient to maintain the solvent to coal ratio at the desired level and/ or to maintain the hydrogen content in digestor 11 at a suiliciently high level. Furthermore, hydrogenation catalyst (from means not shown) may be advantageously used in the digestion step. Make-up hydrogen, if required, is added to the system via line 15. Preferably, the amount of hydrogen present in the digestion zone is from about 1000 to about 100,000 standard cubic feet of hydrogen per barrel of coal-solvent mixture entering digestor 11 via line 8.

The entire eluent from digestion zone 11 is removed vial line 12. This effluent consists of undissolved coal particles, ash, solids, etc., in a very finely dispersed state in admixture with Tetralin solvent, liquid-coal extract and hydrogen gas. This effluent is passed via line 12 to a second separator 13. Within separator 13, which may comprise one or more separation vessels including ilash and fractionation columns, hydrogen gas is removed via line 14, commingled with make-up hydrogen entering via line 15 and passed to digestion zone 11 as hereinbefore described via line 10. At least a portion and preferably all the rst solvent Tetralin is removed via line 16 and is commingled with solvent recovered in the hereinafter described third separation zone 26 entering via line 20 and malke-up solvent entering via 19 and passed via lines 2 and 9 to pulverization zone 5 and digestion Zone 11, respectively, as hereinbefore described.

The eflluent from second separator 13 containing solvent (i.e., Tetralin) not removed therein, liquid-coal extract containing hydrogen-rich and hydrogen-lean componnents and undisolved coal, ash, etc., is removed and passed via line 17 to extraction zone 21. If desired, a portion of this material may be withdrawn via line 18, commingled with line 16 for recycle to digestion zone 11 and/or pulverization zone 5.

Within extraction zone 21, a second separator 13 eflluent (extraction zone feed) is contacted with either a ketone, monocyclic aromatic, cyclohexane, or alkylcyclohexane, selective solvent entering via line 23 under extraction conditions including a temperature of about 150 C., a solvent to extraction zone feed weight ratio of about 3, a. pressure of about 500 p.s.i.g., and preferably in the presence of hydrogen gas added via line 22 at a rate of about 100 s.c.f./barrel of extraction zone 21 feed. Within this zone 21, the selective solvent selectively removes the hydrogen-rich, liquid-coal extraction components from the hydrogen-lean components and undissolved coal, ash, etc., to form a solvent-hydrogen-rich, liquidcoal stream free of solids which is withdrawn via line 25 and passed to second separation zone 26. A residue comprising hydrogen-lean, liquid-coal components and undissolved coal, ash, etc., is withdrawn from extraction zone 21 via line 24 and is disposed of as fuel or source of additional hydrogen through the water gas reaction (means not shown).

Third separation zone 26, comprising a plurality of separation means including fractionation columns, readily operable by those skilled in the art, separates the extraction zones solvent from the hydrogen-rich, liquid-coal extract components such as the naphthenic and napththenicaromatic hydrocarbons and other gasoline boiling range hydrocarbons. Within zone 26, the selective ketone, monocyclic aromatic, or cyclohexane solvent is withdrawn, via line 29; normally gaseous materials, if any, are withdrawn via line .28; hydrogen-rich aromatic and naphthenicaromatic, liquid-coal components suitable for use for further processing and/ or as a solvent for the pulverization and/or digestion zone are withdrawn via line with the net make of light hydrocarbons removed via line 30; and, the higher molecular weight hydrogen-rich components removed via line 27.

The process of the present invention for the conversion of coal into liquid products is further illustrated 1by the following example. This example is, however, not present to limit the process of this invention, but to further illustrate the herein-before described embodiments.

EXAMPLE A gram sample of Pittsburgh seam, bituminous coal was crushed to 100 mesh and smaller size, mixed with 300 grams of Tetralin and placed in an Eppenback colloidal -mill for further size reduction of the particulate coal. The mill was operated for tive hours and produced a coal solvent mixture wherein all of the coal was less less than 100 microns in diameter and 95 wt. percent of the coal was less than two microns in diameter.

The resultant colloided coal-Tetralin mixture was then subjected to the following extraction conditions to convert the coal into liquid products.

Temperature-430 C.

Pressure-2000 p.s.i. g.

Tetralin/coal wt. ratio-3/ l Hydrogen/ coal mixture ratio (scf./bbl.)--4000 Coal residence time-.5 hr.

The resultant liquid extraction product, after centrifuging and removal of excess Tetralin solvent, possessed the following properties:

Molecular weight 503 Hydrogen, wt. percent 7.18 Carbon, wt. percent 87.70 Solids (coal, ash, etc.), wt. percent 0.50

This extraction product is then admixed with benzene in a 5/l benzene to extract Weight ratio and subjected to -a second extraction at C. for a period of l hour. At the completion of this period, the mixture is allowed to cool and settle with t-vvo phases forming a hydrogen-rich upper (benzene) phase and a hydrogenlean lower phase. These phases are separated with 78 wt. percent of the original coal extract contained in the upper benzene phase. The liquid coal contained in the upper phase contains 7.75 wt. percent hydrogen, has an average molecular weight of about 450 and is essentially solid-free (i.e., less than 0.01 wt. percent). The lower, residue containing phase contains 5.52 wt. percent hydrogen, has an average molecular weight of about 1150 and contains essentially Iall of the solids present in the original extraction products.

From the foregoing example, the beneficial import of the process of this invention is readily ascertainable by those trained in the art. Not only are the more valuable hydrogen-rich components separated from the lesser value, hydrogen-lean components but these more valuable components are essentially free of solid coal and ash particles, thus avoiding the cumbersome filtration step utilized by the act. Similar results are also obtained when utilizing ketone type solvents as well as other species of monocyclic aromatic solvents such as toluene, xylenes, etc. and their naphthenic derivatives (cyclohexanes) We claim as our invention:

1. A process for the conversion of solid, ash-containing, coal particles into liquid products which comprises the steps of:

(a) contacting said coal with a first solvent selective for dissolving said coal in a iirst contracting zone under extraction conditions and under hydrogen pressure to produce an etlluent containing a liquid coal extract comprised of hydrogen-rich components and hydrogen-lean components in admixture With said solvent and unconverted coal and ash particles;

(b) separating, from said eluent, at least a portion of said first solvent to produce a stream of coal extract 1 l in admixture with at least a portion of said unconverted coal particles;

(c) contacting said coal extract stream with a` second solvent different than said rst solvent and selective for said hydrogen-rich coal extract components in a second contacting zone at extraction conditions to produce a second zone effluent containing a hydrogen-rich liquid phase and a hydrogen-lean liquid phase, said second solvent being selected from the group consisting of ketones, monocyclic aromatic hydrocarbons, cyclohexane, and alkylcyclohexanes;

(d) separating from said second zone eiuent a hydrogen-rich liquid phase and a hydrogen-lean liquid phase, said second zone hydrogen-rich phase being essentially free of unconverted coal and ash particles.

2. The process of claim 1 further characterized in that said first solvent is a polycyclic aromatic compound.

3. The process of claim 2 further characterized in that said compound is tetrahydronaphthalene.

4. The process of claim 1 further characterized in that said second solvent is la monocyclic aromatic hydrocarbon.

'5. The process of claim 4 further characterized in that said aromatic is benzene.

6. The process of claim 1 further characterized in that said second solvent is a ketone.

7. The process of claim 1 further characterized in that said second solvent is a cyclohexane.

8. A process for the conversion of solid ash-containing coal into liquid products which comprises the steps of (a) admixing coarse size coal with a rst solvent capable of converting coal to liquid products thereby providing a solvent-coarse coal mixture;

(b) passing said mixture to a pulverization zone maintained at pulverization conditions including a temperature of about C. to about 200 C., a pressure of about atmospheric to about 1000 p.s.i.g., a solvent to coal weight ratio of about 0.2 to about 10.0, said pulverization conditions sufficient to produce a pulverized coal-solvent product wherein at least a portion of said coarse coal is reduced to about at least a -8 Tyler standard screen size;

(c) passing lat least a portion of said coal-solvent product to a coal conversion zone maintained at coal conversion conditions and under hydrogen `pressure so as to produce a liquid coal extract product containing unconverted coal, ash and solvent wherein an excess of weight percent of the MAF coal is converted to hydrogen-rich components and hydrogenlean components;

(d) separating from said product at least a portion of said first solvent to produce a stream of coal extract in admixture with at least a portion of said unconverted coal and ash;

(e) contacting said coal extract stream with a second solvent, different than said first solvent and selective for said hydrogen-rich coal components in an extrae tion zone to produce an extraction zone efuent containing a hydrogen-rich liquid phase and a hydrogenlean liquid phase, said second solvent being selected from the group consisting of ketones, monocyclic aromatic hydrocarbons, cyclohexane, and alkylcyclohexanes; and,

(f) separating from said extraction zone effluent a hydrogen-rich liquid phase and a hydrogen-lean liquid phase, said hydrogen-rich phase being essentially free of unconverted coal particles and ash.

9. The process of c1airn-8 further characterized in that said first solvent is a polycyclic aromatic compound.

10. The process of claim 9 further characterized in that said compound is tetrahydronaphthalene.

11. The process of claim y8 further characterized in that said second solvent is a monocyclic aromatic hydrocarbon.

12. The process of claim 11 further characterized in that said aromatic is benzene.

13. The process of claim 8 further characterized in that said second solvent is a ketone.

14. The process of claim 8 further characterized in that said second solvent is a cyclohexane.

References Cited UNITED STATES PATENTS 3,162,594 12/1964 Gorin 208-8 1,822,349 9/ 1931 Jannek 208-8 2,476,999 7/ 1949 Orchin 208-8 3,018,241 1/1962 Gorin 208-8 3,018,242 1/1962 Gorin 208-8 DE-LB-ERT E. GANTZ, Primary Examiner V. O"KEEFE, Assistant Examiner U.S. C1` X.R. 208-337 

